Methods for forming doped silicon oxide thin films

ABSTRACT

The present disclosure relates to the deposition of dopant films, such as doped silicon oxide films, by atomic layer deposition processes. In some embodiments, a substrate in a reaction space is contacted with pulses of a silicon precursor and a dopant precursor, such that the silicon precursor and dopant precursor adsorb on the substrate surface. Oxygen plasma is used to convert the adsorbed silicon precursor and dopant precursor to doped silicon oxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.16/998,338, filed Aug. 20, 2020, which is a continuation of U.S.application Ser. No. 16/702,915, filed Dec. 4, 2019, now U.S. Pat. No.10,784,105, which is a continuation of U.S. application Ser. No.16/192,494, filed Nov. 15, 2018, now U.S. Pat. No. 10,510,530, which isa continuation of U.S. application Ser. No. 15/873,776, filed Jan. 17,2018, now U.S. Pat. No. 10,147,600, which is a continuation of U.S.application Ser. No. 15/402,901, filed Jan. 10, 2017, now U.S. Pat. No.9,875,893, which is a continuation of U.S. application Ser. No.14/846,177, filed Sep. 4, 2015, now U.S. Pat. No. 9,564,314, which is acontinuation of U.S. application Ser. No. 14/184,116, filed Feb. 19,2014, now U.S. Pat. No. 9,153,441, which is a continuation of U.S.application Ser. No. 13/667,541, filed Nov. 2, 2012, now U.S. Pat. No.8,679,958, which claims priority to U.S. Provisional Application No.61/556,033, filed Nov. 4, 2011, and U.S. Provisional Application No.61/620,769, filed Apr. 5, 2012, the disclosures of which areincorporated herein by reference in their entirety.

BACKGROUND Field

The present application relates generally to atomic layer deposition ofdopant films, such as doped silicon oxide thin films.

Background

With the scale down of devices, deposition of dielectric films with goodstep coverage is desirable. Traditional ALD is a self-limiting process,whereby alternated pulses of reaction precursors saturate a substratesurface and leave no more than one monolayer of material per pulse. Thedeposition conditions and precursors are selected to ensureself-saturating reactions, such that an adsorbed layer in one pulseleaves a surface termination that is non-reactive with the additionalgas phase reactants of the same pulse. A subsequent pulse of differentreactants reacts with the previous termination to enable continueddeposition. Thus each cycle of alternated pulses leaves no more thanabout one molecular layer of the desired material. The principles of ALDtype processes have been presented by T. Suntola, e.g. in the Handbookof Crystal Growth 3, Thin Films and Epitaxy, Part B: Growth Mechanismsand Dynamics, Chapter 14, Atomic Layer Epitaxy, pp. 601-663, ElsevierScience B.V. 1994, the disclosure of which is incorporated herein byreference.

As described herein, Atomic Layer Deposition (ALD) processes can be usedto deposit doped silicon oxide, such as BSG and PSG. ALD provides goodstep coverage on three-dimensional structures.

SUMMARY

Dopant thin films can be deposited by atomic layer deposition processesutilizing a dopant precursor and a reactive species. In some embodimentsthe dopant thin film may serve as a solid state diffusion (SSD) layerover a semiconductor substrate, such as in the formation of a finFetstructure.

In accordance with one aspect, methods for forming doped silicon oxidethin films on a substrate in a reaction chamber by atomic layerdeposition (ALD) are provided. In some embodiments the ALD process is aplasma enhanced ALD process (PEALD). In some embodiments the ALD processcomprises providing a pulse of a silicon precursor into a reaction spacecomprising a substrate, providing a pulse of a dopant precursor into thereaction space, removing excess silicon and dopant precursors andcontacting the substrate with a reactive species. In some embodimentsthe reactive species comprises oxygen and may be, for example, oxygenplasma. In some embodiments oxygen gas flows to the reaction chambercontinuously throughout the process. In some embodiments the reactivespecies comprises excited species of nitrogen. The reactants can beprovided in any order and in some embodiments the pulse of the dopantprecursor and the pulse of the silicon precursor at least partiallyoverlap.

In some embodiments, the methods include a doped silicon oxidedeposition cycle comprising: providing a vapor phase first precursorpulse comprising a silicon precursor into the reaction chamber to formno more than about a single molecular layer of the silicon precursor onthe substrate, providing a vapor phase second precursor pulse comprisinga dopant precursor to the reaction chamber such that the dopantprecursor adsorbs in a self-limiting manner on the substrate surface atthe available binding sites, removing excess reactant and any reactionbyproducts from the reaction chamber, providing a vapor phase thirdreactant pulse comprising oxygen plasma, such that the oxygen plasmaconverts the adsorbed silicon and dopant to a doped silicon oxide film.In some embodiments, oxygen flows continuously to the reaction chamberduring the deposition process. Providing the vapor phase third reactantpulse comprises generating a plasma in the flowing oxygen. The oxygenplasma may be generated remotely or in the reaction chamber itself. Insome embodiments the silicon precursor and the dopant precursor areprovided simultaneously. In some embodiments the silicon precursor anddopant precursor are provided in pulses that at least partially overlap.In some embodiments the silicon precursor and the dopant precursor areprovided alternately and sequentially. The deposition cycle is repeateduntil a thin film of a desired thickness and composition is obtained. Insome embodiments, the dopant is selected from boron and phosphorus. Thesilicon precursor may be, for example, BDEAS (bis(diethylamino) silane((C₂H₅)₂N)₂SiH₂).

In some embodiments, a doped silicon oxide film is deposited by a PEALDprocess in which doped silicon oxide and undoped silicon oxidedeposition cycles are provided at a ratio selected to achieve thedesired dopant concentration in the doped silicon oxide film.

In some embodiments, a doped silicon oxide film is deposited by a PEALDprocess in which dopant oxide and undoped silicon oxide depositioncycles are provided at a ratio selected to achieve the desired dopantconcentration in the doped silicon oxide film.

In accordance with another aspect of the present invention, methods forforming a FinFET structure are provided in which a doped silicon oxidefilm or other dopant film is deposited over the Fin by ALD.

In accordance with another aspect, methods of doping a silicon substrateare provided. The methods may comprise depositing a solid statediffusion (SSD) layer comprising a dopant over the surface of thesilicon substrate by atomic layer deposition, depositing a cap layerover the SSD layer, and annealing the substrate to drive dopant from theSSD layer into the underlying silicon substrate. In some embodiments thesubstrate is treated with a plasma prior to depositing the SSD layer. Insome embodiments the SSD layer is deposited by a plasma enhanced ALDprocess, in which the substrate is alternately and sequentiallycontacted with a dopant precursor and a plasma, such as an oxygen,nitrogen, argon, helium, hydrogen or fluorine plasma. The dopant may be,for example, phosphorus, arsenic, antimony, boron, gallium or indium. Insome embodiments two or more of the plasma treatment, the deposition ofthe SSD layer and deposition of the cap layer are carried out in situ.

In accordance with another aspect, methods for depositing dopantcompound films on a substrate in a reaction chamber are provided. TheALD process comprise at least one dopant precursor cycle, wherein apulse of a dopant precursor is provided to the reaction chamber, excessdopant precursor is removed from the reaction chamber and the substrateis contacted with a reactive species such that a dopant compound film isformed. The dopant compound film may comprise a dopant selected fromgroup 13, 14 or 15 elements. In some embodiments the dopant compoundfilm may comprise PN, PC or BC.

For purposes of summarizing embodiments of the invention and some of theadvantages achieved over the prior art, certain objects and advantageshave been described herein above. Of course, it is to be understood thatnot necessarily all such objects or advantages may be achieved inaccordance with any particular embodiment of the invention. Thus, forexample, those skilled in the art will recognize that the invention maybe embodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught herein without necessarilyachieving other objects or advantages as may be taught or suggestedherein.

All of these embodiments are intended to be within the scope of theinvention herein disclosed. These and other embodiments of the presentinvention will become readily apparent to those skilled in the art fromthe following detailed description of the preferred embodiments havingreference to the attached figures, the invention not being limited toany particular preferred embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart generally illustrating a method for forming adoped silicon oxide thin film in accordance with one embodiment.

FIG. 2 is a flow chart generally illustrating the pulsing sequence for amethod of forming a doped silicon oxide thin film.

FIG. 3 is a flow chart generally illustrating the pulsing sequence for amethod of forming a doped silicon oxide thin film.

FIG. 4 is two photomicrographs showing BSG deposited by PEALD, asdescribed herein (left) and as deposited by PECVD (right), on athree-dimensional substrate.

FIG. 5 is an FT-IR spectrum comparing the content of BSG films depositedby PEALD, as described herein, and by PECVD. The FT-IR spectra betweenPEALD and PECVD are almost the same.

FIG. 6 is two photomicrographs showing PSG deposited by PEALD, asdescribed herein (left) and as deposited by PECVD (right), on athree-dimensional substrate.

FIG. 7 is a photomicrograph of a silicon substrate following treatmentwith H₂ plasma.

FIG. 8 is an FT-IR spectrum illustrating the cap effect of a 4 nm SiNcap over a B₂O₃ layer as a function of time. A good cap effect wasobserved.

FIG. 9 illustrates a Si fin structure on which a SSD layer and a caplayer have been deposited.

FIG. 10 illustrates the effect of H₂ plasma pre-treatment on P drive-ininto Si as measured by SIMS.

FIG. 11A illustrates the in-situ cap effect for B aging of a BSG SSDlayer.

FIG. 11B illustrates the effect of the cap on dopant penetration

FIG. 12A illustrates a uniform P dopant concentration in an SSD film.

FIG. 12B compares B dopant concentration in films deposited with astandard recipe and a modulation recipe.

FIG. 12C illustrates B dopant concentration in a dopant film comprisinga monolayer of dopant.

FIG. 13 illustrates a structure utilizing a BSG buffer layer.

FIG. 14 illustrates a structure utilizing a PSG buffer layer.

FIG. 15 illustrates the boron concentration at various depths in asilicon layer following annealing. The same anneal conditions were usedfor all experiments.

FIG. 16 illustrates a reactant pulse flow pattern for forming a BSG orPSG layer.

FIGS. 17A-17C illustrate boron concentration as a function of thecontrol knob (the ratio of boron precursor to silicon precursor).

FIG. 18 shows the provision of boron oxide deposition cycles relative tototal thickness in doped silicon oxide deposition processes.

FIGS. 19A and 19B illustrate a uniform depth profile for P (left) and amodulated depth profile for B in a modulated recipe compared to astandard recipe.

FIGS. 20A-20C illustrate phosphorus concentration as a function of thecontrol knob (ratio of phosphorus precursor to silicon precursor).

FIG. 21A-21F illustrate dopant drive in for B and P following lamp basedRTA anneal and drive in without anneal.

FIG. 22 illustrates a deposition sequence for depositing a PN layer.

FIG. 23 shows the P concentration in a SSD layer structure comprising aPN layer.

FIG. 24 illustrates P concentration in a silicon substrate followingannealing of a PN layer.

DETAILED DESCRIPTION

Thin film layers comprising a dopant, such as solid state doping (SSD)layers can be deposited by plasma-enhanced atomic layer deposition(PEALD) type processes. Doped silicon oxide, for example, has a widevariety of applications, as will be apparent to the skilled artisan. Insome embodiments doped silicon oxide thin films, such as borosilicateglass (BSG) and phosphosilicate glass (PSG) can be deposited on asubstrate by PEALD type processes. In some embodiments dopant thin filmssuch as PN, BN, PC or BC films can be deposited on a substrate by PEALD.ALD can provide good step coverage, as well as precise control of thedopant content. Thus, in some embodiments a dopant thin film isdeposited over a three dimensional structure, such as a fin in theformation of a finFET device. The thickness and composition of thelayers can be controlled to produce a doped silicon oxide film or otherdopant film with the desired characteristics. In some embodiments, adoped silicon oxide film or other dopant layer, such as an SSD layer,can be used as a dopant source for doping a semiconductor. For example,a doped silicon oxide or other dopant layer can be used as a dopantsource to drive dopant into an underlying semiconductor layer, such as asilicon layer. The semiconductor layer to be doped may be, for example,a fin of a finFET device. In some embodiments, the doped silicon oxidelayer is encapsulated with an undoped silicon oxide layer.

The formula of the silicon oxide is generally referred to herein as SiO₂for convenience and simplicity. However, the skilled artisan willunderstand that the actual formula of the silicon oxide can be SiO_(x),where x varies around 2, as long as some Si—O bonds are formed.Generally silicon oxide where Si has an oxidation state of +IV is formedand the amount of oxygen in the material might vary, for example,depending on the dopant content.

ALD type processes are based on controlled, self-limiting surfacereactions. Gas phase reactions are avoided by contacting the substratealternately and sequentially with reactants. Vapor phase reactants areseparated from each other in the reaction chamber, for example, byremoving excess reactants and/or reactant byproducts from the reactionchamber between reactant pulses.

The methods presented herein allow deposition of doped silicon oxidefilms and other dopant films on substrate surfaces. Geometricallychallenging applications are also possible due to the nature of theALD-type processes. According to some embodiments, atomic layerdeposition (ALD) type processes are used to form doped silicon oxidefilms or other dopant films on substrates such as integrated circuitworkpieces.

A substrate or workpiece is placed in a reaction chamber and subjectedto alternately repeated surface reactions. In particular, thin films areformed by repetition of a self-limiting ALD cycle. Preferably, forforming doped silicon oxide films each ALD cycle comprises at leastthree distinct phases. The provision and removal of a reactant from thereaction space may be considered a phase. In a first phase, a firstreactant comprising silicon is provided and forms no more than about onemonolayer on the substrate surface. This reactant is also referred toherein as “the silicon precursor” or “silicon reactant” and may be, forexample, BDEAS. In a second phase, a second reactant comprising a dopantis provided and adsorbs to available binding sites. This second reactantmay also be referred to as a “dopant precursor.” The second reactant maycomprise an element from group 13 (IUPAC new numbering, IIIB accordingto old IUPAC numbering and IIIA according to CAS American numbering),such as boron, an element from group 14 (IUPAC new numbering, IVBaccording to old IUPAC numbering and IVA according to CAS Americannumbering), such as carbon and/or an element from group 15 (IUPAC newnumbering, VB according to old IUPAC European numbering and VA accordingto CAS American numbering), such as phosphorus or arsenic. In someembodiments the second reactant may be, for example, a boron,phosphorous, carbon or arsenic precursor. In a third phase, a thirdreactant comprising a reactive species is provided and may convertadsorbed silicon and dopant precursors to the doped silicon oxide. Insome embodiments the reactive species comprises an excited species. Insome embodiments the reactive species comprises oxygen plasma, oxygenatoms and/or oxygen radicals. In some embodiments the reactive speciescomprises a species of oxygen that is not excited, such as ozone, and isused, for example, in a thermal ALD process. In some embodiments thereactive species comprises ozone. In some embodiments the siliconreactant and/or the dopant reactant comprises oxygen and the reactivespecies does not. In some embodiments the reactive species comprisesexcited species made by plasma discharge. In some embodiments thereactive species comprises nitrogen radicals, nitrogen atoms and/ornitrogen plasma. In some embodiments a reactive species may comprise aHe or Ar plasma. In some embodiments a gas that is used to form a plasmamay flow constantly throughout the process but only be activatedintermittently. Additional phases may be added and phases may be removedas desired to adjust the composition of the final film.

One or more of the reactants may be provided with the aid of a carriergas, such as Ar or He. In some embodiments the silicon precursor and thedopant precursor are provided with the aid of a carrier gas. In someembodiments, two of the phases may overlap, or be combined. For example,the silicon precursor and the dopant precursor may be providedsimultaneously in pulses that partially or completely overlap. Inaddition, although referred to as the first, second and third phases,and the first second and third reactants, the order of the phases may bevaried, and an ALD cycle may begin with any one of the phases. That is,unless specified otherwise, the reactants can be provided in any orderand the process may begin with any of the reactants.

As discussed in more detail below, in some embodiments for depositingdoped silicon oxide, one or more deposition cycles begin with provisionof the silicon precursor, followed by the dopant precursor and areactive oxygen species. In other embodiments, one or more depositioncycles begin with provision of the dopant precursor, followed by thesilicon precursor and the reactive oxygen species. In other embodimentsdeposition may begin with provision of the reactive oxygen species,followed by either the silicon precursor or the dopant precursor.

In some embodiments for forming other types of dopant films each ALDcycle comprises at least two distinct phases. In a first phase, a firstreactant comprising a dopant will form no more than about one monolayeron the substrate surface. This reactant may also be referred to as adopant precursor. The dopant precursor may comprise, for example, anelement from the group 13 (IUPAC new numbering, IIIB according to oldIUPAC numbering and IIIA according to CAS American numbering), such asboron, an element from the group 14 (IUPAC new numbering, IVB accordingto old IUPAC numbering and IVA according to CAS American numbering),such as carbon and/or an element from the group 15 (IUPAC new numbering,VB according to old IUPAC European numbering and VA according to CASAmerican numbering), such as phosphorus or arsenic. In some embodimentsthe second reactant may be for example, a boron, phosphorous, carbonand/or arsenic precursor. In some embodiments the dopant precursorcomprises carbon as well as another dopant, such as an element fromgroup 13 or group 15. For example, the dopant precursor may compriseboron and carbon or phosphorus and carbon. In a second phase a secondreactant comprising a reactive species is provided and converts theadsorbed dopant precursor compound to the dopant film. In someembodiments the reactive species comprises oxygen plasma, oxygen atomsand/or oxygen radicals. In some embodiments the reactive speciescomprises ozone. In some embodiments the reactive species comprisesexcited species made by plasma discharge. In some embodiments thereactive species comprises nitrogen radicals, nitrogen atoms and/ornitrogen plasma. In some embodiments the reactive species comprises Heor Ar plasma. In some embodiments the reactive species is formed byforming a plasma intermittently in a gas that is flowing constantlythroughout the process, such as by forming N plasma intermittently fromflowing N. Additional phases may be added as desired to adjust thecomposition of the film.

Again, one or more of the reactants may be provided with the aid of acarrier gas, such as Ar or He. In some embodiments the dopant precursoris provided with the aid of a carrier gas. In some embodiments, Althoughreferred to as a first phase and a second phase and a first and secondreactant, the order of the phases and thus the order of provision of thereactants may be varied, and an ALD cycle may begin with any one of thephases.

In some embodiments, one or more deposition cycles begin with provisionof the the dopant precursor followed by a reactive species. In otherembodiments, one or more deposition cycles begin with provision of thereactive species followed by the dopant precursor. The reactive speciesis then provided again in the next cycle.

In some embodiments the substrate on which deposition is desired, suchas a semiconductor workpiece, is loaded into a reactor. The reactor maybe part of a cluster tool in which a variety of different processes inthe formation of an integrated circuit are carried out. In someembodiments a flow-type reactor is utilized. In some embodiments ahigh-volume manufacturing-capable single wafer ALD reactor is used. Inother embodiments a batch reactor comprising multiple substrates isused. For embodiments in which batch ALD reactors are used, the numberof substrates is preferably in the range of 10 to 200, more preferablyin the range of 50 to 150, and most preferably in the range of 100 to130.

Exemplary single wafer reactors, designed specifically to enhance ALDprocesses, are commercially available from ASM America, Inc. (Phoenix,Ariz.) under the tradenames Pulsar® 2000 and Pulsar® 3000 and ASM JapanK.K (Tokyo, Japan) under the tradename Eagle® XP and XP8. Exemplarybatch ALD reactors, designed specifically to enhance ALD processes, arecommercially available from and ASM Europe B.V (Almere, Netherlands)under the tradenames A4ALD™ and A412™.

In some embodiments, if necessary, the exposed surfaces of the workpiececan be pretreated to provide reactive sites to react with the firstphase of the ALD process. In some embodiments a separate pretreatmentstep is not required. In some embodiments the substrate is pretreated toprovide a desired surface termination. In some embodiments the substrateis pretreated with plasma.

The reaction chamber is typically purged between reactant pulses. Theflow rate and time of each reactant, is tunable, as is the purge step,allowing for control of the dopant concentration and depth profile inthe film.

As mentioned above, in some embodiments, a gas is provided to thereaction chamber continuously during each deposition cycle, or duringthe entire ALD process, and reactive species are provided by generatinga plasma in the gas, either in the reaction chamber or upstream of thereaction chamber. In some embodiments the gas is oxygen. In otherembodiments the gas may be nitrogen, helium or argon. The flowing gasmay also serve as a purge gas for the first and/or second precursor, aswell as for the reactive species. For example, flowing oxygen may serveas a purge gas for a first silicon precursor and a second dopantprecursor, as well as for reactive oxygen species. In some embodimentsnitrogen, argon or helium may serve as a purge gas for a dopantprecursor and a source of excited species for converting the dopantprecursor to the dopant film.

The cycle is repeated until a film of the desired thickness andcomposition is obtained. In some embodiments the deposition parameters,such as the flow rate, flow time, purge time, and/or precursorsthemselves, may be varied in one or more deposition cycles during theALD process in order to obtain a film with the desired characteristics.In some embodiments, hydrogen and/or hydrogen plasma are not provided ina deposition cycle, or in the deposition process.

The term “pulse” may be understood to comprise feeding reactant into thereaction chamber for a predetermined amount of time. The term “pulse”does not restrict the length or duration of the pulse and a pulse can beany length of time.

In some embodiments, the silicon precursor is provided first. After aninitial surface termination, if necessary or desired, a first siliconprecursor pulse is supplied to the workpiece. In accordance with someembodiments, the first precursor pulse comprises a carrier gas flow anda volatile silicon species, such as BDEAS, that is reactive with theworkpiece surfaces of interest. Accordingly, the silicon precursoradsorbs upon the workpiece surfaces. The first precursor pulseself-saturates the workpiece surfaces such that any excess constituentsof the first precursor pulse do not further react with the molecularlayer formed by this process.

The first silicon precursor pulse is preferably supplied in gaseousform. The silicon precursor gas is considered “volatile” for purposes ofthe present description if the species exhibits sufficient vaporpressure under the process conditions to transport the species to theworkpiece in sufficient concentration to saturate exposed surfaces.

In some embodiments the silicon precursor pulse is from about 0.05 toabout 5.0 seconds, about 0.1 to about 3 s or about 0.2 to about 1.0 s.

After sufficient time for a molecular layer to adsorb on the substratesurface, excess first precursor is then removed from the reaction space.In some embodiments the excess first precursor is purged by stopping theflow of the first chemistry while continuing to flow a carrier gas orpurge gas for a sufficient time to diffuse or purge excess reactants andreactant by-products, if any, from the reaction space. In someembodiments the excess first precursor is purged with the aid of oxygengas that is flowing throughout the ALD cycle.

In some embodiments, the first precursor is purged for about 0.1 toabout 10 s, about 0.3 to about 5 s or about 0.3 to about 1 s. Provisionand removal of the silicon precursor can be considered the first orsilicon phase of the ALD cycle.

A second, dopant precursor is pulsed into the reaction space to contactthe substrate surface. The dopant precursor may be provided with the aidof a carrier gas. The dopant precursor may be, for example, a boronprecursor, such as triethyl boron (TEB) or trimethyl boron (TMB), or aphosphorous precursor, such as trimethylphosphite (TMPI). The precursorpulse is also preferably supplied in gaseous form. The dopant precursoris considered “volatile” for purposes of the present description if thespecies exhibits sufficient vapor pressure under the process conditionsto transport the species to the workpiece in sufficient concentration tosaturate exposed surfaces.

In some embodiments, the dopant precursor pulse is about 0.05 to about5.0 s, 0.1 to about 3.0 s or 0.2 to about 1.0 s.

After sufficient time for a molecular layer to adsorb on the substratesurface at the available binding sites, the second dopant precursor isthen removed from the reaction space. In some embodiments the flow ofthe second chemistry is stopped while continuing to flow a carrier gasfor a sufficient time to diffuse or purge excess reactants and reactantby-products, if any, from the reaction space, preferably with greaterthan about two reaction chamber volumes of the purge gas, morepreferably with greater than about three chamber volumes. In someembodiments the purge gas is an oxygen gas that is flowing continuouslythroughout the ALD process. Provision and removal of the dopantprecursor can be considered the second or dopant phase of the ALD cycle.

In some embodiments, the dopant precursor is purged for about 0.1 toabout 10.0 s, 0.3 to about 5.0 s or 0.3 to 1.0 s. The flow rate and timeof the dopant precursor pulse, as well as the purge step of the dopantphase, are tunable to achieve a desired dopant concentration and depthprofile in the doped silicon oxide film. Although the adsorption of thedopant precursor on the substrate surface is self-limiting, due to thelimited number of binding sites, pulsing parameters can be adjusted suchthat less than a monolayer of dopant is adsorbed in one or more cycles.

In the third phase, reactive species, such as oxygen plasma is providedto the workpiece. Oxygen, O₂, is flowed continuously to the reactionchamber during each ALD cycle in some embodiments. Oxygen plasma may beformed by generating a plasma in oxygen in the reaction chamber orupstream of the reaction chamber, for example by flowing the oxygenthrough a remote plasma generator.

Typically, the oxygen plasma is provided for about 0.1 to about 10seconds. In some embodiments oxygen plasma is provided for about 0.1 toabout 10 s, 0.5 to about 5 s or 0.5 to about 2.0 s. However, dependingon the reactor type, substrate type and its surface area, the oxygenplasma pulsing time may be even higher than 10 seconds. In someembodiments, pulsing times can be on the order of minutes. The optimumpulsing time can be readily determined by the skilled artisan based onthe particular circumstances.

Oxygen plasma may be generated by applying RF power of from about 10 toabout 1000 W, preferably from about 30 to about 500 W, more preferablyfrom about 50 to about 300 W in some embodiments. The RF power may beapplied to oxygen that flows during the oxygen plasma pulse time, thatflows continuously through the reaction chamber, and/or that flowsthrough a remote plasma generator. Thus in some embodiments the plasmais generated in situ, while in other embodiments the plasma is generatedremotely.

After a time period sufficient to completely saturate and react thepreviously adsorbed molecular layer with the oxygen plasma pulse, anyexcess reactant and reaction byproducts are removed from the reactionspace. As with the removal of the first two reactants, this step maycomprise stopping the generation of reactive species and continuing toflow the oxygen for a time period sufficient for excess reactive speciesand volatile reaction by-products to diffuse out of and be purged fromthe reaction space. In other embodiments a separate purge gas may beused. The purge may, in some embodiments, be from about 0.1 to about 10s, about 0.1 to about 4 s or about 0.1 to about 0.5 s. Together, theoxygen plasma provision and removal represent a third phase in a dopedsilicon oxide atomic layer deposition cycle, and can also be consideredthe oxidation phase.

The three phases together represent one ALD cycle, which is repeated toform doped silicon oxide thin films of the desired thickness. While theALD cycle is generally referred to herein as beginning with the siliconphase, it is contemplated that in other embodiments the cycle may beginwith the dopant phase or with the oxidation phase. One of skill in theart will recognize that the first precursor phase generally reacts withthe termination left by the last phase in the previous cycle. Thus,while no reactant may be previously adsorbed on the substrate surface orpresent in the reaction space if the oxidation phase is the first phasein the first ALD cycle, in subsequent cycles the oxidation phase willeffectively follow the silicon phase. In some embodiments one or moredifferent ALD cycles are provided in the deposition process.

In some embodiments, a doped silicon oxide ALD cycle comprises a siliconphase, a dopant phase and an oxidation phase. The silicon phasecomprises providing a pulse of BDEAS to a reaction chamber comprising asubstrate. Excess BDEAS is removed and the substrate is contacted with apulse of a dopant precursor in the dopant phase. The dopant precursormay be, for example, a pulse of a boron dopant precursor, for exampletriethyl boron (TEB) or a pulse of a phosphorus dopant precursor, suchas trimethylphosphite (TMPI). Excess dopant precursor and reactionby-products, if any, are removed. The substrate is then contacted withoxygen plasma to form a boron or phosphorous-doped silicon oxide. Theoxygen plasma may be generated in situ, for example in an oxygen gasthat flows continuously throughout the ALD cycle. In other embodimentsthe oxygen plasma may be generated remotely and provided to the reactionchamber.

As mentioned above, each pulse or phase of each ALD cycle is preferablyself-limiting. An excess of reactants is supplied in each phase tosaturate the susceptible structure surfaces. Surface saturation ensuresreactant occupation of all available reactive sites (subject, forexample, to physical size or “steric hindrance” restraints) and thusensures excellent step coverage. In some embodiments the pulse time ofone or more of the reactants can be reduced such that completesaturation is not achieved and less than a monolayer is adsorbed on thesubstrate surface. However, in some embodiments the dopant precursorstep is not self-limiting, for example, due to decomposition or gasphase reactions.

As discussed above, in some embodiments, an ALD process begins with thesilicon phase, followed by the dopant phase and, in turn, the oxidationphase. However, in other embodiments the dopant phase is first, followedby the silicon phase and the oxidation phase. For example, the substratemay first be contacted with a pulse of a boron dopant precursor, forexample triethyl boron (TEB) or a pulse of a phosphorus dopantprecursor, such as trimethylphosphite (TMPI). Excess dopant precursor isremoved. The substrate is then contacted with a silicon precursor, suchas BDEAS. Excess silicon precursor and reaction by-products, if any, areremoved. The substrate is then contacted with an oxygen plasma to form aboron or phosphorous-doped silicon oxide. The oxygen plasma may begenerated in situ, for example in an oxygen gas that flows continuouslythroughout the ALD cycle, or remotely.

In some embodiments, the silicon precursor and the dopant precursor areboth provided prior to any purge step. Thus, in some embodiments a pulseof silicon precursor is provided, a pulse of dopant precursor isprovided, and any unreacted silicon and dopant precursor is purged fromthe reaction space. The silicon precursor and the dopant precursor maybe provided sequentially, beginning with either the silicon precursor orthe dopant precursor, or together. In some embodiments, the siliconprecursor and dopant precursor are provided simultaneously. The ratio ofthe dopant precursor to the silicon precursor may be selected to obtaina desired concentration of dopant in the deposited thin film.

After removal of unreacted silicon and dopant precursor, reactivespecies or excited species, such as ozone or oxygen radicals, oxygenatoms or oxygen plasma may be generated, such as in flowing oxygen gas,and are contacted with the substrate. Again, in some embodiments oxygengas may be flowing continuously to the reaction space during the ALDcycle. In other embodiments the excited species, such as oxygen radicalsmay be generated remotely. The reactive species or excited species reactwith adsorbed silicon and dopant precursor, forming a layer of dopedsilicon oxide.

FIG. 1 is a flow chart generally illustrating a doped silicon oxide ALDdeposition cycle that can be used to deposit a doped silicon oxide thinfilm in accordance with some embodiments. According to one embodiment, adoped silicon oxide thin film is formed on a substrate by an ALD typeprocess comprising multiple doped silicon oxide deposition cycles, eachdoped silicon oxide deposition cycle 100 comprising:

contacting a substrate with a vaporized silicon compound 110 such thatthe silicon compound adsorbs on the substrate surface;

contacting the substrate with a vaporized dopant precursor compound 120;and

contacting the substrate with oxygen plasma 130, thereby converting theadsorbed silicon compound and dopant precursor compound into dopedsilicon oxide. Oxygen may flow continuously throughout the cycle, withoxygen plasma formed at the appropriate times to convert adsorbedsilicon compound and dopant precursor into doped silicon oxide.

As mentioned above, in some embodiments the substrate may be contactedsimultaneously with the silicon compound and the dopant precursorcompound, while in other embodiments these reactants are providedseparately.

The contacting steps are repeated 140 until a thin film of a desiredthickness and composition is obtained. Excess reactants may be purgedfrom the reaction space after each contacting step.

FIG. 2 is a flow chart generally illustrating another doped siliconoxide ALD cycle for forming a doped silicon oxide thin film inaccordance with some embodiments. According to such embodiments, a dopedsilicon oxide thin film is formed on a substrate by an ALD type processcomprising multiple doped silicon oxide deposition cycles, each dopedsilicon oxide deposition cycle 200 comprising:

contacting the substrate with a vaporized dopant precursor compound 210;

removing excess dopant precursor 215;

contacting the substrate with a vaporized silicon compound 220 such thatthe silicon compound adsorbs to the substrate;

removing excess silicon compound 225; and

contacting the substrate with oxygen plasma 230, thereby converting theadsorbed silicon compound and dopant precursor compound into dopedsilicon oxide. In some embodiments oxygen may flow continuouslythroughout the cycle, with oxygen plasma formed at the appropriate timesto convert adsorbed silicon compound and dopant precursor into dopedsilicon oxide. In some embodiments, oxygen plasma may be generatedremotely.

The contacting steps are repeated 240 until a thin film of a desiredthickness and composition is obtained.

As mentioned above, in some embodiments, the silicon precursor anddopant precursor may be provided either sequentially or simultaneously,without an intervening purge step. Such an embodiment is illustrated inFIG. 3 , in which a doped silicon oxide thin film is formed on asubstrate by an ALD type process comprising multiple doped silicon oxidedeposition cycles 300 comprising:

contacting the substrate with a vaporized dopant precursor compound anda vaporized silicon compound 310 such that the dopant compound andsilicon compound adsorb to the substrate;

removing excess dopant precursor and silicon compound 315; and

contacting the substrate with oxygen plasma 320, thereby converting theadsorbed silicon compound and dopant precursor compound into dopedsilicon oxide. The cycle may be repeated 330 one or more times. In someembodiments the oxygen may flow continuously throughout the cycle, withoxygen plasma formed intermittently to convert the adsorbed siliconcompound and dopant precursor into the doped silicon oxide. In someembodiments oxygen plasma is generated remotely and provided to thereaction space.

As discussed above, the deposition process typically comprises multipleALD deposition cycles. In some embodiments, the dopant precursor isprovided in every deposition cycle. In other embodiments, however, thedopant precursor may be provided in only a portion of the depositioncycles. Cycles in which dopant precursor is provided may be calleddopant precursor cycles, while cycles in which dopant is not providedmay be called silicon precursor cycles. In some embodiments a siliconprecursor is also provided in the dopant precursor cycles, as describedabove. An exemplary silicon precursor cycle may comprise, for example,alternately and sequentially contacting the substrate with a siliconprecursor and an oxygen reactant. In some embodiments the siliconprecursor is the same reactant that is used in a dopant precursor cycle,while in some embodiments the silicon precursor may be different. Insome embodiments the oxygen reactive species is the same as that used inthe dopant precursor cycle, while in other embodiments a differentoxygen reactive species may be used.

The ratio of silicon precursor cycles to dopant precursor cycles may beselected to control the dopant concentration in the ultimate filmdeposited by the PEALD process. For example, for a low dopant density,the ratio of dopant precursor cycles to silicon precursor cycles may beon the order of 1:10. For a higher concentration of dopant, the ratiomay range up to about 1:1 or higher such as 1.5:1, 2:1, 2.5:1, 3:1, 4:1etc. . . . . In some embodiments all of the deposition cycles in an ALDprocess may be dopant precursor cycles. The ratio of deposition cyclescomprising dopant to deposition cycles that do not include dopant (suchas the ratio of dopant precursor cycles to silicon precursor cycles, orthe ratio of dopant oxide cycles to silicon precursor cycles) may bereferred to as the control knob. For example, if one dopant precursorcycle is provided for every four silicon precursor cycles, the controlknob is 0.25. If no undoped oxide cycles are used, the control knob maybe considered to be infinite.

By controlling the ratio of dopant precursor cycle to silicon precursorcycle, the dopant concentration can be controlled from a density rangeof about 0 atoms of dopant to about 5 E22/cm³ atoms of dopant. Densitymay be measured, for example, by SIMS (secondary-ion-probe massspectrometry). For B and P doped films, this upper range is close toB₂O₃ or P₂O₅.

In addition, the dopant density can be varied across the thickness ofthe film by changing the ratio of dopant precursor cycles to siliconprecursor cycles during the deposition process. For example, a highdensity of dopant may be provided near the substrate surface (lowerratio of silicon precursor cycles to dopant precursor cycle), such asnear a Si surface (corresponding to the bottom of the doped siliconoxide surface, such as a BSG or PSG surface) and the density of dopantat the top surface away from the substrate may be low (higher ratio ofsilicon precursor cycles to dopant precursor cycles). In otherembodiments a high density of dopant may be provided at the top surfacewith a lower density near the substrate surface.

In some embodiments, a doped silicon oxide layer is formed by providinga dopant precursor cycle at certain intervals in a silicon oxidedeposition process. The interval may be based, for example, on cyclenumber or thickness. For example, one or more dopant precursordeposition cycles may be provided after each set of a predeterminednumber of silicon precursor deposition cycles, such as after every 10,20, 50, 100, 200, 500 etc. . . . undoped silicon oxide depositioncycles. In some embodiments undoped silicon oxide deposition cycles maybe repeated until a silicon oxide layer of a predetermined thickness isreached, at which point one or more dopant precursor cycles are thencarried out. This process is repeated such that dopant is incorporatedin the film at specific thickness intervals. For example, one or moredopant precursor cycles may be provided after each 5 nm of undoped SiO₂that is deposited. The process is then repeated until a doped siliconoxide thin film of a desired thickness and composition has beendeposited.

In some embodiments in an ALD process for producing doped silicon oxidefilms, one or more “dopant oxide” deposition cycles are provided alongwith undoped silicon oxide deposition cycles. The process may alsoinclude one or more doped silicon oxide deposition cycles.

In the “dopant oxide” deposition cycles, the silicon precursor isomitted from the doped silicon oxide deposition cycles described above.Thus, the substrate is exposed to alternating and sequential pulses ofdopant precursor and an oxidant, such as oxygen plasma. Other reactiveoxygen sources may be used in some embodiments. In some embodiments, adoped silicon oxide film is provided by conducting multiple dopant oxidedeposition cycles and multiple silicon oxide deposition cycles. Theratio of dopant oxide cycles to silicon precursor cycle may be selectedto control the dopant concentration in the ultimate doped silicon oxidefilm. For example, for a low dopant density, the ratio of dopant oxidecycles to silicon precursor cycle may be on the order of 1:10. In otherembodiments a high dopant density is achieved by increasing the ratio ofdopant oxide cycles to silicon precursor cycle to 1:1 or even higher,such as 1.5:1, 2:1, 2.5:1, 3:1, 4:1 etc. . . . . For example, for a highdopant density, such as a high B density, the ratio of dopant oxidecycles to silicon precursor cycle may be on the order of 6:1, or even10:1.

Here too, the density can be varied across the thickness of the film bychanging the ratio of dopant oxide cycles to silicon oxide cycles duringthe deposition process. For example, a high density of dopant may beprovided near the substrate surface by using a lower ratio of siliconoxide cycles to dopant oxide cycles and the density of dopant at the topsurface may be lower by providing a higher ratio of silicon oxide cyclesto dopant oxide cycles.

As discussed above, in other embodiments, a dopant film that is not adoped silicon oxide is deposited by an ALD process. For example, thefilm may be a PN film, a BN film, a BC film or a PC film. According tosome embodiments, a dopant thin film is formed on a substrate by an ALDtype process, such as a PEALD process, comprising multiple depositioncycles, each deposition cycle comprising:

contacting the substrate with a vaporized dopant precursor;

removing excess dopant precursor; and

contacting the substrate with a reactive species, thereby converting theadsorbed dopant precursor into the dopant film.

The dopant precursor may be provided with the aid of a carrier gas. Thedopant precursor may be, for example, a boron precursor, such astriethyl boron (TEB), or a phosphorous precursor, such astrimethylphosphite (TMPI). The dopant precursor pulse is also preferablysupplied in gaseous form. The dopant precursor is considered “volatile”for purposes of the present description if the species exhibitssufficient vapor pressure under the process conditions to transport thespecies to the workpiece in sufficient concentration to saturate exposedsurfaces.

In some embodiments, the dopant precursor pulse is about 0.05 to about5.0 s, 0.1 to about 3.0 s or 0.2 to about 1.0 s.

After sufficient time for a molecular layer to adsorb on the substratesurface at the available binding sites, the excess dopant precursor isthen removed from the reaction space. In some embodiments the flow ofthe dopant precursor is stopped while continuing to flow a carrier gasfor a sufficient time to diffuse or purge excess reactants and reactantby-products, if any, from the reaction space. In some embodiments thepurge gas is flowing continuously throughout the ALD process. Provisionand removal of the dopant precursor can be considered the dopant phaseof the ALD cycle, as discussed above.

In some embodiments, the dopant precursor is purged for about 0.1 toabout 10.0 s, 0.3 to about 5.0 s or 0.3 to 1.0 s.

The flow rate and time of the dopant precursor pulse, as well as thepurge step of the dopant phase, are tunable to achieve a desired dopantconcentration and depth profile in the dopant film. Although theadsorption of the dopant precursor on the substrate surface isself-limiting, due to the limited number of binding sites, pulsingparameters can be adjusted such that less than a monolayer of dopant isadsorbed in one or more cycles.

In the second phase, reactive species, such as plasma is provided to theworkpiece. The plasma may be, for example, nitrogen, argon or heliumplasma. Plasma may be generated as described elsewhere herein and may begenerated remotely or in situ. In some embodiments, the reactive speciesmay contribute one or more species to the dopant film. For example,nitrogen may be contributed by a reactive species comprising nitrogen.

Typically, the reactive species is provided for about 0.1 to about 10seconds. However, depending on the reactor type, substrate type and itssurface area, the pulsing time may be even higher than 10 seconds. Insome embodiments, pulsing times can be on the order of minutes. Theoptimum pulsing time can be readily determined by the skilled artisanbased on the particular circumstances.

After a time period sufficient to completely saturate and react thepreviously adsorbed molecular layer with the reactive species, anyexcess reactive species and reaction byproducts are removed from thereaction space. This step may comprise stopping the generation ofreactive species and continuing to flow a gas from which the reactivespecies were generated or carrier gas for a time period sufficient forexcess reactive species and volatile reaction by-products to diffuse outof and be purged from the reaction space. In other embodiments aseparate purge gas may be used. The purge may, in some embodiments, befrom about 0.1 to about 10 s, about 0.1 to about 4 s or about 0.1 toabout 0.5 s. Together, the reactive species provision and removalrepresent a second phase in a dopant film atomic layer deposition cycle,and can also be considered the reactive species phase.

The two phases together represent one ALD cycle, which is repeated toform dopant thin films of the desired thickness. Additional reactantsand/or additional phases may be added to achieve a desired composition.While the ALD cycle is generally referred to herein as beginning withthe dopant phase, it is contemplated that in other embodiments the cyclemay begin with the reactive species phase. One of skill in the art willrecognize that the first precursor phase generally reacts with thetermination left by the last phase in the previous cycle. Thus, while noreactant may be previously adsorbed on the substrate surface or presentin the reaction space if the reactive species phase is the first phasein the first ALD cycle, in subsequent cycles the reactive species phasewill effectively follow the dopant phase. In some embodiments one ormore different ALD cycles are provided in the deposition process.

Deposition temperatures are maintained below the thermal decompositiontemperature of the reactants but at a high enough level to avoidcondensation of reactants and to provide the activation energy for thedesired surface reactions. Of course, the appropriate temperature windowfor any given ALD reaction will depend upon the surface termination andreactant species involved. Here, the temperature is preferably at orbelow about 400° C. In some embodiments the deposition temperature isabout 20 to about 400° C., about 50 to about 400° C. or about 100 toabout 400° C.

The deposition processes can be carried out at a wide range of pressureconditions, but it is preferred to operate the process at reducedpressure. The pressure in the reaction chamber is typically from about0.1 Pa to about 50000 Pa or more. However, in some cases the pressurewill be higher or lower than this range, as can be readily determined bythe skilled artisan. The pressure in a single wafer reactor ispreferably maintained between about 50 Pa and 1000 Pa, preferablybetween about 100 and 600 Pa and more preferably between about 150 Paand 500 Pa. In some embodiments, the pressure in a batch ALD reactor ispreferably maintained between about 0.1 Pa and 70 Pa, more preferablybetween about 4 Pa and about 25 Pa.

The reactant source temperature, such as the silicon source temperature,is preferably set below the deposition or substrate temperature. This isbased on the fact that if the partial pressure of the source chemicalvapor exceeds the condensation limit at the substrate temperature,controlled layer-by-layer growth of the thin film is compromised.

In some embodiments, the silicon source temperature is from about 20 toabout 150° C. In some embodiments the silicon source temperature isgreater than about 60° C. during the deposition. For example, in somesingle wafer processes the silicon source may be between about roomtemperature and about 100° C. The dopant precursor source may be atabout the same temperature. In some embodiments, where greater doses areneeded, for example in batch ALD, the silicon source temperature is fromabout 90° C. to about 200° C., preferably from about 130° C. to about170° C.

In some embodiments the growth rate of the thin films, such as thinfilms comprising doped silicon oxide is preferably from about 0.8 toabout 2.0 Å/cycle. In other embodiments the growth rate is about 1.0 toabout 1.5 Å/cycle.

In some embodiments the deposited thin films comprising doped siliconoxide have a refractive index from about 1.6 to about 1.9 (as measuredwith a wavelength of 633 nm). In some embodiments the refractive indexof BSG or PSG is about 1.48 as measured at 633 nm.

In some embodiments, the deposited thin films, such as the doped siliconoxide thin films, are deposited on a three dimensional structure andhave step coverage of greater than about 80%, greater than about 90%,greater than about 95% or step coverage of about 100%.

In some embodiments the deposited films, such as the films comprisingsilicon oxide, have a step coverage of more than 80%, in otherembodiments preferably more than 90% and in other embodiments preferablymore than 95%.

In some embodiments the thin films, such as the doped silicon oxidefilms, are deposited to a thickness of 5 nm or less or 10 nm or less.However, in some situations dopant thin films, such as doped siliconoxide films, of greater thickness, such as 10 nm or more, 30 nm or more,50 nm or more or even 100 nm or more may be deposited. The specificthickness can be selected by the skilled artisan based on the particularcircumstances.

Source Materials

In general, the source materials, (e.g., silicon source materials anddopant source materials), are preferably selected to provide sufficientvapor pressure, sufficient thermal stability at substrate temperature,and sufficient reactivity of the compounds for effecting deposition byALD. “Sufficient vapor pressure” typically supplies enough sourcechemical molecules in the gas phase to the substrate surface to enableself-saturated reactions at the surface at the desired rate. “Sufficientthermal stability” typically means that the source chemical itself doesnot form growth-disturbing condensable phases on the surface or leaveharmful level of impurities on the substrate surface through thermaldecomposition. In other words, temperatures are kept above thecondensation limits and below the thermal decomposition limits of theselected reactant vapors. One aim is to avoid uncontrolled condensationof molecules on the substrate. “Sufficient reactivity” typically resultsin self-saturation in pulses short enough to allow for a commerciallyacceptable throughput time. Further selection criteria include theavailability of the chemical at high purity and the ease of handling ofthe chemical.

In some embodiments the silicon precursor is an aminosilane or anaminesilane.

In some embodiments the silicon precursor comprises aminosilane, wherethe silicon is bonded to one nitrogen atom and three hydrogen atoms. Forexample, the silicon precursor may comprise dialkylaminesilane,(R₂N)Si—H₃.

In some embodiments the silicon precursor comprises a silicon amine,where silicon is bonded to two nitrogen atoms and two hydrogen atoms.For example, the silicon precursor may comprise bis(dialkylamine)silane,(R₂N)₂Si—H₂. In some embodiments the silicon precursor comprisesBDEAS(=bis(diethylamino)silane).

In some embodiments the silicon precursor comprises a silicon amine,where silicon is bonded to three nitrogen atoms and one hydrogen atom.For example, the silicon precursor may comprisetris(dialkylamine)silane, (R₂N)₃Si—H₁.

In some embodiments, the silicon precursor comprises a silicon amine,where silicon is bonded to four nitrogen atoms. For example, the siliconprecursor may comprise tetrakis(dialkylamine)silane, (R₂N)₄Si.

Organic compounds having a Si—Si bond and an NH_(x) group eitherattached directly to silicon (to one or more silicon atoms) or to acarbon chain attached to silicon are used in some embodiments. In someembodiments, the silicon precursor may comprise an aminodisilane, suchas hexakis(ethylamino)disilane. In some embodiments the silicon compoundmay have the formula:

R^(III) _(3-x)(R^(II)R^(I)N)_(x)Si—Si(N—R^(I)R^(II))_(y)R^(III) _(3-y),

wherein the

x is selected from 1 to 3;

y is selected from 1 to 3;

R^(I) is selected from the group consisting of hydrogen, alkyl, andsubstituted alkyl;

R^(II) is selected from the group consisting of alkyl and substitutedalkyl; and

R^(III) is selected from the group consisting of hydrogen, hydroxide(—OH), amino (—NH₂), alkoxy, alkyl, and substituted alkyl;

and wherein the each x, y, R^(III), R^(II) and R^(I) can be selectedindependently from each other.

In some embodiments the silicon compound ishexakis(monoalkylamino)disilane:

(R^(II)—NH)₃Si—Si(NH—R^(II))₃

In other embodiments the silicon compound is (CH₃—O)₃Si—Si(O—CH₃)₃

In some embodiments the dopant precursor is a boron compound. Exemplaryboron compounds include boron alkoxide compounds, such as B(OR)₃ andalkylboron compounds, such as BR₃. In some embodiments the dopantprecursor is trimethylboron (B(CH₃)₃) or triethylboron (B(C₂H₅)₃).

In some embodiments the dopant precursor is a phosphorous compound.Exemplary phosphorous compounds include phosphorous alkoxides, such asP(OR)₃ and alkylphosphorous compounds, such as PR₃. In some embodimentsthe dopant precursor is trimethylphosphor: P(CH₃)₃. In some embodimentsPH₃ can be used.

In some embodiments the dopant precursor is an arsenic compound. Inother embodiments the dopant precursor is a carbon compound. Exemplaryarsenic compounds include AsH₃ and alkylarsenic compounds, such asAs₂(CH₃)₄. Exemplary carbon compounds include alcohols C_(x)H_(y)OH andhydrocarbons C_(x)H_(y).

As discussed above, in some embodiments oxygen plasma is used as thereactive oxygen source. Oxygen plasma may be generated in the reactionchamber, for example from O₂ that is flowed into the reaction chamber.In some embodiments oxygen plasma is generated in the vicinity of thesubstrate, for example above the substrate. In some embodiments oxygenplasma is generated outside of the vicinity of the substrate. Forexample, oxygen plasma may be generated remotely, outside of thereaction chamber. In some embodiments thermal ALD is used and reactivespecies of oxygen, for example ozone or nitrogen oxides NO_(N), whereinx is from about 0.5 to about 3, which are not excited, are used.

SSD Layer Structures

In some embodiments the dopant films deposited by the methods disclosedherein can be used in solid state doping (SSD) layer stacks. FIG. 9shows an example of an SSD layer stack for FinFet device manufacturing.The Si fin is typically fabricated from a Si wafer. The wafer with theSi fin structure is transferred to ALD process module, where a first ALDprocess is used for depositing the SSD layer. A second depositionprocess can then be used to deposit a cap layer, as illustrated in FIG.9 . In some embodiments the first and second processes are conductedwithout an air break; that is, in-situ sequential deposition of SSDlayer and cap layer is carried out.

In some embodiments an in-situ plasma pre-treatment of the substrate isconducted before SSD layer deposition to enhance doping efficiency intothe Si fin. FIG. 10 shows the effect of H₂ plasma pre-treatment on Pdrive-in into Si as measured by SIMS. The original SSD layer was a 5 nmthick layer of PSG deposited by PEALD and having a P concentration of 7wt % (2.8E+21at/cm3). The cap layer was a 5 nm thick SiO layer depositedby PEALD. The rapid thermal anneal condition was 4 sec at 1000 deg-C ina N₂ atmosphere. The PSG with H₂ plasma pre-treatment sample showed ahigher P drive-in level and a shallow diffusion depth. The H₂ plasmapre-treatment can provide some tuning space for FinFet device design.The pre-treatment is not limited only H₂ plasma. In some embodiments thepre-treatment plasma may be selected from Ar, He, H₂, Fluorinecontaining gas and their mixed gas plasma.

As illustrated in FIG. 9 and discussed above, in some embodiments a caplayer is deposited over the dopant layer. In some embodiments the caplayer is directly over and contacting the dopant layer. The cap layermay comprise, for example, SiO or SiN. In some embodiments the cap layercomprises an oxide or nitride of a group 13, 14 or 15 element. FIG. 11Aillustrates the in-situ cap effect for B aging of a BSG SSD layer. It iswell known that B concentration in high dopant level BSG decrease overtime with exposure to air. In FIG. 11A the vertical axis indicatesrelative B concentration in a BSG SSD layer as calculated from FTIR B-Opeak area. For this test, a BSG SSD layer was deposited using CK=10 andhad a B concentration of ˜1.2E22atoms/cm³. The B concentration isnormalized by B-O peak area of an as-deposited BSG sample. The Bconcentration in BSG samples without cap and with a soft cap (here aPEALD SiO cap layer with a thickness of 5 nm deposited by using lowpower; 50 w) decreased immediately after deposition with exposure toair. On the other hand, BSG samples with a robust cap (here a PEALD SiOcap layer with a thickness of 5 nm deposited by using high power; 500 w)maintained >80% of the initial B concentration. FIG. 11B illustrates theeffect of the cap on dopant depth.

The cap is not limited only to SiO films but can also be other films,such as SiN, SiON, P(B)N, P(B)ON, etc. . . . and their stack isconsiderable such as SSD film with PN (or BN) and SiN (or SiO) stackcap.

One example of a cap layer of a material other than SiO is illustratedin FIG. 8 . FIG. 8 is a FT-IR graph showing that 4 nm of SiN is enoughto maintain the B-O peak of an under layer of BO even after a 12 hexposure to air. The film thickness is one important parameter tomaintain B concentration in an SSD layer. In FIG. 8 , a 4 nm film wassufficient to maintain B concentration but a 2 nm did not maintain Bconcentration as well. Thus, the film thickness for a cap layer may beselected, in part, in view of cap film quality. As illustrated in FIG.11A, the film quality may affect the cap capability. Thinner filmthickness, such as 1 nm, may be used with a good quality film tomaintain the B concentration in SSD layer. In some embodiments the caplayer is from about 1 to about 10 nm, and may be about 4 nm or greater.

The depth profile of the dopant in the SSD layer can be selected basedon FinFet device design. For example, uniform concentration in an SSDfilm is shown in FIG. 12A, a modulated concentration in an SSD film isshown FIG. 12B, and a monolayer (one pulse chemical adsorption) is shownFIG. 12C. The PSG layer with uniform depth profile shown in FIG. 12A wasdeposited by using the reaction conditions in Table 5, below. Themodulated depth profile for the BSG film shown in FIG. 12B as the“modulation recipe” was deposited using the condition in Table 4, below,and the pulse interval in FIG. 18 . The initial B concentration (nearthe interface between the Si substrate and SSD film) is higher than theB concentration at the SSD film surface (away from the Si substrate).This film is effective to realize high concentration and shallowdiffusion into a Si substrate. This profile is easily tuned by adjustingthe dopant precursor pulse ratio and interval taking into account devicedesign requirements.

In some embodiments a single monolayer of dopant is deposited. Oneexample of the depth profile for such a monolayer is shown in FIG. 12C.Here, the monolayer was deposited by using Condition 1 in Table 3,below. The single monolayer of dopant is effective to provide extremelyshallow diffusion into a Si substrate when this is indicated by devicedesign. The dopant precursor is flowed in to the process module afterpre-treatment only one time to form a chemisorbed dopant monolayer onthe Si surface. The SSD monolayer is capped, for example by PEALD SiO.

Buffer Layer Structure

In some embodiments, the dopant thin film, such as a doped silicondioxide, can be used as a buffer layer during doping of a siliconsubstrate by annealing a dopant oxide layer. For example a doped silicondioxide buffer layer may be used between a dopant layer, such as adopant oxide layer and a cap layer, such as a SiN cap layer. The bufferlayer may reduce or prevent dopant diffusion from the underlying dopantlayer into structures overlying the buffer layer. Thus, dopant isdirected into the underlying silicon substrate during annealing. Thismay be used, for example, to increase dopant density without having tomodify the anneal conditions. In some embodiments the doped siliconoxide buffer layer structure is formed on a silicon substrate, forexample on a FinFet device. Although illustrated primarily in terms of adoped silicon oxide buffer layer, other dopant layers may be used anddeposited as described herein.

An exemplary boron doped silicon oxide buffer layer structure isillustrated in FIG. 13 . An exemplary phosphorus doped silicon oxidebuffer layer structure is illustrated in FIG. 14 . As discussed below,the structure comprises a H₂ plasma treated silicon substrate, anoverlying dopant oxide layer, which serves as a source of dopant that isdriven into the silicon layer during an anneal, a doped silicon oxidebuffer layer to reduce or prevent diffusion of dopant into overlyingstructures, and a cap layer that can reduce or prevent moisture frominteracting with the dopant oxide, which may be hygroscopic.

In some embodiments, a structure such as those illustrated in FIGS. 13and 14 is formed. First, a silicon substrate is treated with plasma,such as H₂ plasma. The plasma treatment may create surface roughness andremoves the native oxide. This may facilitate dopant penetration intothe silicon substrate. A silicon surface treated with H₂ plasma is shownin FIG. 7 . As mentioned above, in some embodiments the plasma treatmentand subsequent deposition processes may be carried out in situ.

Second, a dopant oxide layer is deposited directly over and contactingthe treated substrate. In the examples illustrated in FIGS. 13 and 14 ,B₂O₃ and P₂O₅ layers are used, respectively. The dopant oxide layercomprises more dopant (such as P or B) than an overlying doped silicondioxide layer. The dopant oxide layer may be deposited by ALD, forexample using multiple dopant oxide deposition cycles as describedherein. However, in other embodiments, other types of deposition may beused, such as thermal CVD. In some embodiments the dopant oxide layer isfrom about 1 to about 10 nm thick, or about 2 nm thick. In someembodiments the dopant oxide layer may be deposited in situ with thedoped silicon oxide layer and/or the cap layer.

Third, a dopant layer such as a doped silicon dioxide buffer layer isdeposited directly over and contacting the doped oxide layer. In theexamples illustrated in FIGS. 13 and 14 , BSG and PSG are deposited,respectively. Deposition of the doped silicon dioxide layer may beessentially as described elsewhere herein. In some embodiments the dopedsilicon oxide layer is about 1 to 10 nm thick, or about 3 nm thick.

A cap layer, such as a SiN cap layer is then deposited over the bufferlayer. The cap layer may be directly over and contacting the bufferlayer, as illustrated in FIGS. 13 and 14 . The dopant oxide layers inthe structure may have hygroscopic properties and the cap layer mayreduce the interaction of any moisture with the underlying doped silicondioxide buffer layer and/or the dopant oxide layer. As mentioned above,FIG. 8 is an FT-IR graph showing that 4 nm of SiN is enough to preventan underlying B₂O₃ layer from reacting with moisture. In someembodiments the cap layer is from about 1 to about 10 nm, and may beabout 4 nm or greater. In some embodiments a SiN cap layer of about 4 nmthick is used.

In some embodiments, for example as described above, a doped silicondioxide layer serves as a dopant source. For example, in someembodiments a doped silicon dioxide layer alone is deposited over asilicon substrate and annealed to drive dopant into the siliconsubstrate. The doped silicon dioxide layer may be, for example, BSG orPSG.

In some embodiments a dopant oxide layer (such as B₂O₃ or P₂O₅) isdeposited over a silicon substrate and a dopant silicon dioxide layer(such as BSG or PSG) is deposited over the dopant oxide and thestructure annealed to drive boron into the underlying silicon substrate.

In some embodiments a further cap layer, such as a SiN cap layer, isdeposited over the dopant silicon dioxide layer prior to annealing.

In some embodiments, the silicon substrate is treated with plasma, suchas H₂ plasma, prior to depositing the dopant oxide layer and/or dopedsilicon dioxide layer. The plasma treatment can remove native oxide, ifpresent, and/or increase surface roughness (as illustrated in FIG. 7 ),thus making it easier to drive dopant into the silicon substrate.

FIG. 15 illustrates the difference in dopant density (here, boron)following annealing of a BSG layer only over a silicon substrate,annealing of a BSG layer over a H₂ plasma surface-treated siliconsubstrate, and annealing of a structure as illustrated in FIG. 13 (aB₂O₃ layer deposited over H₂ plasma surface-treated silicon substrateand BSG buffer layer over the B₂O₃ layer).

The following non-limiting examples illustrate certain embodiments.

Example 1

BSG was deposited by PEALD and PECVD on a silicon wafer. The siliconsource was BDEAS and the boron source was trimethyl borate or triethylborate. As illustrated in FIG. 4 and in Table 1 below, PEALD BSG showsgood step coverage. An FT-IR spectrum of PEALD and PECVD BSG is shown inFIG. 5 .

Dopant density was measured by SIMS and dopant density uniformity wasmeasured at 9 points on the wafer.

TABLE 1 BSG deposited by PEALD Step Step Boron density Si Boron coveragecoverage uniformity source source Side/Top Bottom/Top (± %) BDEASTrimethyl Borate 100 100 <10 BDEAS Triethyl Borate  95 100 <10

Example 2

PSG was deposited by PEALD and PECVD on a silicon wafer. The siliconsource was BDEAS and the phosphorus source was trimethylphosphite. Asillustrated in FIG. 6 , and shown in Table 2 below, PEALD PSG shows goodstep coverage.

Dopant density was measured by SIMS and dopant density uniformity wasmeasured at 9 points on wafer.

TABLE 2 PSG deposited by PEALD Phosphorus Step Step density SiPhosphorus coverage coverage uniformity source source Side/TopBottom/Top (±%) BDEAS Trimethylphosphite 100 100 < 10

Example 3

BSG or PSG is deposited by PEALD, using the pulsing sequence illustratedin FIG. 16 . As illustrated, a reactant flow is maintained throughoutthe deposition process. The reactant may be, for example 02. First, thesilicon source gas, such as BDEAS, is supplied for about 0.5 s by FPS.The reaction chamber is purged for about 1 s, for example by continuingthe flow of the reactant as illustrated. A dopant source gas, such asthe illustrated B or P source, is provided, for example for about 0.5 s.The dopant source gas is purged for about 1 s, for example by continuingto flow the reactant as illustrated. RF plasma is provided, for examplefor about 1 s. The plasma may be generated in the flowing reactant, asillustrated, for example by applying power of about 50 W and about 300Pa. The reaction chamber may then be purged again, such as by continuingto flow the reactant, without generating a plasma. The purge may be, forexample, about 0.5 s. The cycle is repeated to deposit a boron orphosphorous doped silicon oxide film of a desired thickness.

Example 4

BSG was deposited by PEALD using various ratios of boron oxidedeposition cycles to undoped silicon oxide deposition cycles. In someexperiments the control knob ranged from 0.001 to infinite, siliconoxide cycles were from 10 to 1000 and films with a thickness of about0.5 nm to about 30 nm were deposited.

Briefly, a silicon substrate was placed in a reaction chamber and oxygenwas flowed through the reaction chamber continuously during the process.In each undoped silicon oxide deposition cycle, a silicon precursor,BDEAS, was pulsed into the reaction chamber for 0.3 s. Silicon precursorwas purged for 0.8 s and RF power was applied for 0.4 s to generateoxygen reactive species, such oxygen excited species in flowing oxygengas, followed by a further 0.1 s purge. In each boron oxide depositioncycle, a boron precursor, trimethyl borate, was pulsed into the reactionchamber for 0.4 s, followed by a 5 s purge. RF power was applied for 0.4s, followed by a further 0.1 s purge.

Three exemplary deposition processes are described in Table 3 below inwhich the control knob ranged from 0.00167 (600 silicon oxide depositioncycles to 1 boron oxide deposition cycle) to infinite (no silicon oxidedeposition cycles and 1000 boron cycles).

TABLE 3 SiO B doped Control Total cycles cycles Knob Thickness cycleConditon-1 600    1 0.00167  30 nm  601 Condition-2  10   10 1       0.5nm   20 Condition-3   0 1000 Infinite   5 nm 1000

The concentration of boron at different control knob settings (ratios ofboron oxide cycles to silicon oxide cycles) is illustrated in FIG.17A-C. Process 1 and Process 2 (FIG. 17A) are described in Table 4. Byvarying the ratio of cycles, different concentrations of boron can beachieved in the BSG layer.

TABLE 4 Conditions for BSG deposition by Process 1 and 2 Process1Process2 Susceptor Temp 300 deg C. 300 deg C. Electrode Gap 14.5 mm 14.5mm Press 200 Pa 200 Pa RF Power 50 W 500 W Oxidant gas 500 sccm 500 sccmSi Precursor carrier gas 2000 sccm 2000 sccm Dopant Precursor carriergas 2000 sccm 2000 sccm Si Precursor Feed 0.3 0.3 Si Precursor Purge 0.80.8 RF ON 0.4 0.4 Post Purge 0.1 0.1 B Precursor Feed 0.4 0.4 BPrecursor Purge 5.0 5.0 RF ON 0.4 0.4 Post Purge 0.1 0.1

In some experiments, the boron oxide deposition cycle was provided atintervals during the deposition process, as shown in FIG. 18 , where thesquares and triangles indicate dopant cycle provision. In the STD Recipeexperiments (FIG. 18 , squares), dopant cycles were provided at regularintervals. In particular, the undoped silicon oxide cycle was repeateduntil 0.5 nm of silicon oxide was deposited. A single boron oxide cyclewas then carried out. Subsequently, a single boron oxide depositioncycle was provided after every additional 1.0 nm of silicon oxide untila 5 nm film had been deposited. Deposition cycles were essentially asdescribed above.

In other experiments, additional boron oxide cycles were providedearlier in the deposition process, as shown for the Modulation Recipe inFIG. 18 (triangles). As can be seen in FIG. 18 , three boron oxidedeposition cycles were provided during the deposition of the first 0.5nm of silicon oxide. Additional boron oxide deposition cycles wereprovided when the film reached 1.5 nm and 4 nm. Again, deposition cycleswere essentially as described above.

FIGS. 19A and B show the dopant concentration as a function of depth forfilms with a uniform depth profile (FIG. 19A) and films deposited by theSTD recipe and the Modulation recipe described above (FIG. 15B).

Example 5

PSG was deposited by PEALD using various ratios of phosphorous oxidedeposition cycles to undoped silicon oxide deposition cycles werecarried out. The process conditions are described in Table 5 below.Briefly, a silicon substrate was placed in a reaction chamber and oxygenwas flowed through the reaction chamber continuously during the process.In each undoped silicon oxide deposition cycle, a silicon precursor,BDEAS, was pulsed into the reaction chamber for 0.3 s. Silicon precursorwas purged for 0.8 s and RF power was applied for 0.4 s to generateoxygen reactive species in the flowing oxygen gas, followed by a further0.1 s purge. In each phosphorous oxide deposition cycle, a phosphorousprecursor, trimethylphosphite, was pulsed into the reaction chamber for0.4 s, followed by a 5 s purge. RF power was applied for 0.4 s, followedby a further 0.1 s purge. A total of 90 deposition cycles was used formost experiments, producing films about 5 nm thick.

The concentration of phosphorous at different control knob settings(ratios of phosphorous oxide cycles to silicon oxide cycles) isillustrated in FIGS. 20A-C. By varying the ratio of cycles, differentconcentrations of phosphorous can be achieved in the PSG layer.

TABLE 5 PSG deposition conditions CK1 Susceptor Temp 300 degC ElectrodeGap 14.5 mm Press 200 Pa RF Power 50 W Oxidant gas 500 sccm Si Precursorcarrier gas 2000 sccm Dopant Precursor carrier gas 2000 sccm SiPrecursor Feed 0.3 Si Precursor Purge 0.8 RF ON 0.4 Post Purge 0.1 PPrecursor Feed 0.3 P Precursor Purge 2.0 RF ON 0.4 Post Purge 0.1

A PSG film formed using a ratio of one phosphorus oxide versus oneundoped silicon oxide cycles (a control knob of 1.00) was analyzedfurther. FIG. 19A shows the phosphorous concentration as a function ofdepth in the thin film.

Example 6

PSG was deposited on a silicon substrate by PEALD using the conditionsin Example 5. Following deposition, and without annealing the film, aHF-dip was used to remove the PSG layer (FIG. 21D). Phosphorusconcentration was measured as a function of depth (FIG. 21E). FIG. 21Eshows that phosphorus does not significantly penetrate into theunderlying silicon substrate during deposition of the PSG layer.

Example 7

PSG was deposited on a silicon substrate by PEALD using the conditionsin Table 6 below.

TABLE 6 PSG deposition conditions PSG CK1 Susceptor Temp 300 deg C.Electrode Gap 14.5 mm Press 200 Pa RF Power 50 W Oxidant gas 500 sccm SiPrecursor carrier gas 2000 sccm Dopant Precursor carrier gas 2000 sccmSi Precursor Feed 0.3 Si Precursor Purge 0.8 RF ON 0.4 Post Purge 0.1 PPrecursor Feed 0.3 P Precursor Purge 2.0 RF ON 0.4 Post Purge 0.1

A lamp based rapid thermal anneal for 3 s at 1000° C. was used to driveboron into the substrate (FIG. 21A). Annealing conditions are providedin Table 7 below. Following anneal, the doped silicon oxide layer wasremoved by HF-dip (FIG. 21A) and the phosphorous concentration atvarious depths in the substrate was measured (FIG. 21C). FIG. 21Cillustrates the penetration of phosphorus into the substrate followingthe anneal.

TABLE 7 Anneal conditions Tool Mattson3000 Anneal Temp. 1000 deg C. GasN2 Anneal Time 3 sec Press 1 atm Transfer temp 600 deg C.

BSG films were also deposited and annealed. BSG films were depositedusing the conditions in Table 8, below, and subsequently annealed usingthe conditions in Table 7. However, the substrate was treated with H₂plasma prior to BSG deposition. H₂ plasma treatment conditions areprovided in Table 9. FIG. 21F illustrates the measured boronconcentration as a function of depth in the deposited film, and showsthat boron does not significantly penetrate into the underlying siliconsubstrate during deposition of the BSG layer.

TABLE 8 BSG deposition conditions BSG CK2 Susceptor Temp 300 deg C.Electrode Gap 14.5 mm Press 200 Pa RF Power 50 W Oxidant gas 500 sccm SiPrecursor carrier gas 2000 sccm Dopant Precursor carrier gas 2000 sccmSi Precursor Feed 0.3 Si Precursor Purge 0.8 RF ON 0.4 Post Purge 0.1 BPrecursor Feed 0.3 B Precursor Purge 5.0 RF ON 0.4 Post Purge 0.1

TABLE 9 Pre-treatment Conditions Susceptor Temp 300 deg C. Electrode Gap14.5 mm Press 350 Pa RF Power 400 W H2 1000 sccm Ar 1000 sccm Trt Time30 sec.

Following annealing and HF-dip, boron concentration was measured as afunction of depth. The results are illustrated in FIG. 21B, which showsthe penetration of boron into the substrate following the anneal.

Example 8

PN was deposited on a silicon substrate by PEALD using TMPI as the Pprecursor and N plasma as the reactive species. The depositionconditions are provided in Table 10, below. Nitrogen flowed constantlyand RF power was provided intermittently to create a plasma, as shown inFIG. 22 . A growth rate of 0.015 nm/cycle was observed and the PN filmhad a uniformity of about 5% and a refractive index of about 1.66. Insome experiments a SiN cap layer was deposited on the PEALD PN layer.FIG. 23 shows the P concentration relative to depth in the depositedfilm stack, as measured by SIMS. FIG. 24 shows P concentration in the Sisubstrate after annealing, as measured by SIMS.

TABLE 10 Susceptor Temp 200 deg C. Electrode Gap 7.5 mm Press 400 Pa RFPower 800 W N2 flow 2000 sccm TMPI carrier Ar flow 2000 sccm P precursorfeed 0.3 sec P Precursor Purge 1 .0 sec RFON 0.2 sec Post Purge 0.1 sec

We claim:
 1. A method for depositing doped silicon oxide on a substratein a reaction chamber comprising at least one doped silicon oxidedeposition cycle comprising, in order: contacting the substrate with adopant precursor; contacting the substrate with a first reactivespecies; contacting the substrate with a silicon precursor; exposing thesubstrate to a purge gas; and contacting the substrate with a secondreactive species.